The ultimate objective is to determine how chlamydiae are able to infect and colonize human mucosal epithelial cells. Chlamydial pathogenesis is characterized by a unique intracellular developmental cycle which is initiated when a single elementary body is endocytosed and terminates when infectious progeny is released into the environment upon cell death. The events preceding release and those preceding entry will be investigated. We will initially characterize two genetic loci which contain genes, called crp, encoding three distinct developmentally regulated cysteine-rich outer membrane proteins. The nucleotide sequence of each gene will be determined for three representative Chlamydia trachomatis serovars. The structure-function relationship of one of the crp gene products will be examined by utilizing a novel expression system which involves the 'exposition' of specific antigenic determinants at the surface of Escherichia coli. We will also examine the regulatory mechanism by analysis of crp-specific messenger RNA. The molecular mechanisms underlying endocytosis of the infectious elementary body will be studied by using a liposome reconstitution assay to identify adhesin(s) and an in vitro invasion assay to identify molecule(s) involved in entry. Substrates will include whole chlamydiae, purified chlamydial outer membrane proteins, and recombinants carrying exposed chlamydial virulence determinants. Chlamydial diseases are increasingly recognized as major health problems throughout the world. The identification and characterization of chlamydial genes encoding developmental products and virulence determinants will further the development of new reagents for the diagnosis, treatment and/or prevention of chlamydial infections.